Symmetrix remote-data-facility

Symmetrix Remote Data Facility
Product Description Guide Enterprise Storage Software

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SYMMETRIX REMOTE DATA FACILITY PRODUCT DESCRIPTION GUIDE
Symmetrix Remote Data Facility (SRDF)
Product Description Guide
Table of Contents 3 Chapter 1: Introduction
3 Overview
3 The Value of Symmetrix Remote Data Facility
4 Business Impact
4 Operational Impact
5 Financial Impact
5 EMC’s Architectures for Enterprise Storage: ISA and MOSAIC:2000
6 Information Protection
7 Information Sharing
7 Information Management
8 SRDF and Symmetrix
9 SRDF and Fibre Channel
9 SRDF and IP
10 SRDF and EMC TimeFinder
10 SRDF and AS/400 Environments
11 Chapter 2: SRDF Uses and Applications
11 Overview
11 Disaster Recovery, the Old Way
11 Disaster Scenarios
12 Disaster Recovery Sites
12 Traditional Techniques for Data Recovery
12 Store the Tape Copies at a Secure Site
13 Create the Tape Copies at the Recovery Site
13 Data Copies on Disk
13 Using the Host/Server to Create the Copies
13 Disaster Recovery Testing
13 Business Continuity
14 Eliminating the “Race to Sunrise”
14 Loading Data Warehouses
14 Scheduled Maintenance
14 Data Center Migrations
14 Workload Migrations
14 AS/400 Applications
16 Growing Your Business with SRDF
16 SRDF Over IP Optimizes Information Deployment
16 SRDF Over Fibre Channel Increases Throughput
17 Chapter 3: SRDF Detailed Description
17 SRDF Principles of Operation
17 SRDF Hardware Components
19 SRDF Implementation

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Chapter 1
Introduction
Overview This guide describes Symmetrix Remote Data Facility, SRDF™
, EMC’s industry-leading
information protection and business continuity software solution for use with Symmetrix®
enterprise storage systems.
Chapter 1 provides an overview of SRDF, its capabilities, and its beneﬁts for today s information-
centric enterprises. The chapter also includes a general discussion of Symmetrix, EMC’s intelligent
enterprise storage system, the Symmetrix architecture, and EMC’s other information protection,
information sharing, and information management solutions. The remaining chapters provide a
greater level of detail and operational description on the material presented in Chapter 1.
The Value of Symmetrix EMC Enterprise Storage™
helps you realize your most aggressive business goals through
Remote Data Facility intelligent information sharing, management, and protection. Achieving those goals is what we
call experiencing The EMC Effect™
. Symmetrix Remote Data Facility helps you achieve The EMC
Effect by providing you with complete business continuity that can accelerate your business in the
new E-based economy. With SRDF the data center is secure from both unforeseen disasters and
planned events such as daily backups, database loads and refreshes, application testing, scheduled
maintenance, and data center migrations or consolidations. Equally important, EMC has
expanded SRDF’s capabilities to include Virtual Private Networks using the Internet Protocol (IP),
and Fibre Channel technology.
SRDF is the only solution providing automatic information protection/business continuity
simultaneously to mainframe, UNIX®
, Windows NT®
, and AS/400®
systems. SRDF offers a
host-independent, mirrored data storage solution that duplicates production or source site data on
a physically separate recovery or target site transparently to users, applications, databases, and
host processors.
When primary (that is, source) stored data is unavailable, SRDF enables fast switchover to the
target copy data so that critical information is again available in minutes. Business operations and
related applications resume full functionality with minimal interruption. Source and target site
Symmetrix systems can be adjacent to one another or thousands of miles apart. In either case, the
same enterprise-level information protection capabilities are afforded. After such an event, SRDF
can resynchronize data to the source or to the target, at the users’ discretion, thereby ensuring
information and database consistency.
SYMMETRIX A SYMMETRIX B
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20 Installation and Planning
20 Supported Environments
21 Multihost Support
22 SRDF Campus Solution
23 SRDF Extended Distance Solutions
23 SRDF FarPoint
23 SRDF Multi-hop Capability
24 SRDF over IP for Extended Distances
24 SRDF Modes of Operation
24 Synchronous Mode
25 Semi-Synchronous Mode
26 Adaptive Copy Mode
26 Consistency Group Utility
27 Domino Option
27 SRDF FarPoint Option
27 Invalid Tracks Attribute
27 SRDF Management
28 Chapter 4: SRDF Usability Considerations
28 SRDF Features and Capabilities
28 Sequential Data Updates Across the Link
28 Local and Remote Mirrors of the Same Volume
28 SRDF and RAID-S Compatibility
28 Dynamic Sparing
28 Source/Target Switching
29 Source Control of Target
29 HP MetroCluster
30 Potential Events
30 Local or Remote Volumes
30 Link Breaks
30 Return to Source Site
31 Synchronization and Resynchronization
31 Use of Track Tables
32 Performance
32 Data Recovery
32 Databases
33 Backup Using Remote Data
33 Read-Only Access to Target Volumes
33 SRDF Testing
34 Chapter 5: Symmetrix Software Solutions and Service
34 Software Solutions
35 Professional Services
35 Enterprise Business Continuity
36 Enterprise Storage Architecture and Design ñ Building an E-Infostructure
36 Enterprise Storage Network
36 Support and Service

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Financial Impact Direct impact on the revenue-generating and service-providing aspects of SRDF includes:
• Elimination of expensive and inflexible manual backup and restore procedures.
• Improved cost-effectiveness through direct Symmetrix-to-Symmetrix operation — CPU
redundancy is unnecessary and performance is enhanced.
• Savings in telecommunication costs using SRDF over IP networks.
• High throughput and connectivity characteristics of Fibre Channel improving local and campus
data protection and replication.
• Cost-effective resource utilization ó a single SRDF target site can support multiple source sites,
each with multiple hosts.
• Immediate return on SRDF investment justified by preventing just one extended outage.
EMC’s Architectures EMC Enterprise Storage systems and solutions are built on the foundation of Intelligent Storage
for Enterprise Storage: Architecture (ISA) and MOSAIC:2000®
— a combination of industry-standard software and
ISA and MOSAIC:2000 hardware — to achieve unsurpassed levels of information protection, information sharing, and
information management. EMC’s Enterprise Storage architecture ensures optimum performance,
availability, scalability, and connectivity. Complementary ISA software and MOSAIC:2000
hardware architectures demonstrate the unique storage system philosophy of all EMC Enterprise
Storage products working together to solve our customers’ biggest IT challenges.
An EMC Enterprise Storage system:
• Stores and retrieves data from all major computing platforms, including mainframe and open
systems environments.
• Enables software-based functionality that ensures business continuity even in the event of a disaster.
• Delivers rapid and non-disruptive data migration from one system to another.
• Shares information, regardless of origin.
EMC’s Intelligent Storage Architecture, ISA, consolidates information sharing, management, and
protection into a single intelligent storage system capable of managing the information storage and
retrieval needs of the entire enterprise.
SRDF
Database Applications Management
Information Management
Provides graphical user
interfaces to make configuration
and management of
storage activity easy.
Information Sharing
Multihost support allows
high-speed movement of large
amounts of information between
different platforms.
APIs
Information Protection
Ensuring the highest availability
in the event of planned or
unplanned information systems
interruptions.
Performance,
Availability
Maintainability,
Scalability, Compatibility
MOSAIC:2000
Connectivity
Without SRDF, planned or unplanned events can disrupt data center operations and prevent access
to vital business data. Business, operational, and financial losses can be significant. SRDF helps
protect against these losses and their impact on your enterprise. Besides offering data protection,
SRDF over IP capitalizes on e-focused business trends, while Fibre Channel connectivity offers
high-speed, efficient and effective data transfers in local or campus configurations. Using SRDF
dramatically impacts any organization’s business, operations, and finances.
•1 Business Impact
•2 Operational Impact
•3 Financial Impact
Business Impact SRDF’s unique capabilities enable:
• Enhanced customer service due to reduced planned and unplanned downtime.
• Faster recovery from planned and unplanned downtime, increasing the availability of revenue-
generating applications.
• Deployment of underutilized IP networking structure for low cost information access to local and
remote sites.
• Support for Fibre Channel architecture, thus expanding connectivity options for open systems and
Symmetrix to Symmetrix data mirroring.
• Longer running of transactional applications, resulting in increased revenue.
• Additional business applications and opportunities gained from higher data availability.
• Incremental uses of remotely mirrored data.
Operational Impact SRDF improves enterprise processes by streamlining operations, enhancing efficiency, and
protecting business assets. SRDF enables:
• Improved disaster recovery procedures through the elimination of slow, labor-intensive tape-based
retrieval and loading schemes.
• Increased throughput for business-critical information with high-speed Fibre Channel
• Ability to deploy remote copies of files and databases to previously inaccessible sites using
IP networks.
• More frequent and less costly online testing of disaster recovery scenarios, providing confidence in
a viable and flexible solution.
• Simultaneous support of heterogeneous mainframe, UNIX, Windows NT, and AS/400 systems,
reducing complexity and simplifying IS staff training requirements.
• Database integrity consistently maintained and preserved through built-in synchronization
functionality.
• No special coding or software applications required, simplifying its use.

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• EMC CopyCross is optional mainframe-based software that intercepts data originally targeted for
tape systems and redirects it onto Symmetrix. Once on Symmetrix it can be SRDF’s to a remote
Symmetrix for disaster recovery purposes. The result is a fast post-disaster restart for tape-based
data — as fast as any other disk-based data. Customers avoid waiting for the arrival of physical
computer tapes. Instead, they work with Symmetrix disk images of the same information.
Information Sharing EMC Enterprise Storage systems provide a centralized, shareable information repository in
support of changing environments and mission-critical applications. This leading-edge technology
begins with physical devices shared between heterogeneous operating environments and extends to
specialized software that enhances information sharing between disparate platforms.
• Symmetrix provides standard simultaneous multiple system support
• EMC Enginuity Operating Environment™
makes it possible for Symmetrix systems to serve as the
foundation for a scalable, open and manageable information storage infrastructure
• Symmetrix Enterprise Storage Platform (ESP) software provides simultaneous mainframe and
open systems support for Symmetrix storage systems
• EMC Celerra™
is unique hardware and software that brings unprecedented levels of availability,
management, and scalability to network file storage
• EMC InfoMover™
, formerly known as Symmetrix Multihost Transfer Facility (SMTF), facilitates
high speed bulk file transfers between heterogeneous host platforms without the need for
network resources
• Application Programming Interfaces (APIs) enable customers and third-party vendors to tightly
integrate their software solutions with hardware and software from EMC
Information Management EMC Enterprise Storage systems improve information management by allowing users to
consolidate storage capacity for multiple hosts and servers. EMC offers powerful graphical user
interface (GUI)-based tools that dramatically simplify and enhance Symmetrix monitoring
and control.
• EMC Data Manager (EDM™
), a combined hardware and software system, supports open system
backup needs from one centrally managed site while offering a complete, high-performance
database backup solution for the entire enterprise.
• EMC PowerPath™
offers a combination of simultaneous multiple path access, workload balancing,
and path failover capabilities between Symmetrix systems and supported server hosts.
• EMC ControlCenter provides extensive user control, performance monitoring of data in real time,
error condition identification, and configuration management of Symmetrix systems in mainframe
and open system environments.
MOSAIC:2000 combines industry-standard hardware with optimized software to provide the
highest performance, availability, scalability, and performance.
EMC’s architectural approach lets you easily integrate the enhancements that advances in software
and hardware technology offer. The basic system infrastructure remains constant when you add or
replace elements. This adaptability allows EMC Enterprise Storage to remain on the leading
edge of user needs and technology improvements while preserving existing information
technology investments.
Information Protection In addition to Symmetrix Remote Data Facility, EMC also provides a variety of other hardware
and software information protection features. These include extensive RAID (Redundant Array of
Independent Disks) data protection, Mirroring (the optimum RAID level for both performance
and availability), EMC’s RAID-S enhanced parity protection, and Dynamic Sparing. EMC
Symmetrix also affords automatic ‘phone home’ diagnostic capabilities so that failing parts can be
replaced before they become troublesome.
Other integrated and optional EMC information protection software and service offerings include
the following:
• SRDF FarPoint™
, an advanced SRDF capability, significantly increases SRDF performance over
extended distances through the optimization of the communication line.
• EMC TimeFinder™
provides the optional capability for system administrators to create, in
background mode, independently addressable Business Continuance Volumes (BCVs) that can be
used to run other tasks simultaneously with normal production activities. This capability is known
as “workload compression.”
• EMC Foundation Suite by Veritas and EMC Database Edition for Oracle by Veritas. Both of these
suite products are tightly integrated with EMC TimeFinder, providing parallel BCV operations to
Veritas File System and Volume Manager users.
• Symmetrix Data Migration Services (SDMS™
) is an optional EMC service that enables users to
migrate large or small volumes of data off heterogeneous mainframe storage devices or other
Symmetrix systems to new Symmetrix systems without stopping business operations during
the migration.
• EMC CopyPoint™
is optional software that works with SRDF to extend SRDF capabilities in
AS/400 environments.

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SRDF adds business continuity protection to Symmetrix’s standard information protection
features. All SRDF protection features are available for Symmetrix systems whether in support of
mainframe, open systems, or heterogeneous environments.
SRDF extends business continuity protection by providing separate copies of data on physically
separate Symmetrix systems. If data becomes unavailable on one Symmetrix, it can be accessed by
the other Symmetrix system(s).
SRDF and Fibre Channel For sites requiring a higher level of throughput and real-time mirroring, EMC offers SRDF within
the Fibre Channel (FC) architecture. Fibre Channel increases SRDF throughput significantly. Fibre
Channel affords major benefits to enterprise storage in terms of consolidation, distance between
Symmetrix SRDF sites, connectivity, and performance. Together, SRDF and Fibre Channel boost
the throughput performance of existing technologies as well as provide great flexibility for
open systems.
EMC offers a fully integrated, highly available Fibre Channel-based Enterprise Storage Network
(ESN) system called the EMC Connectrix™
system. The single enclosure Connectrix system houses
either one or two Fibre Channel directors supporting up to 64 Fibre Channel ports, a service
processor, connectivity management application software, and an efficient cable management
system. The highly modular and scalable system offers an array of configuration choices for a
variety of connectivity and availability requirements. ESN provides significant advantages in terms
of information consolidation, connectivity, multi-host support, and ease of management. Using
SRDF in combination with Connectrix means that SRDF Symmetrix to Symmetrix transfers as
well as host to Symmetrix transfers occur through an Enterprise Storage Network (ESN) using
Fibre Channel protocol. SRDF, Connectrix, and Fibre Channel technologies provide a capable
foundation for your storage architecture while serving as the basis for future business and
technology expansion.
SRDF and IP SRDF now enables the automatic replication of data and applications between geographically
separated EMC Symmetrix Enterprise Storage Systems over Virtual Private Networks using the
Internet Protocol (IP). This unique feature takes advantage of the ubiquitous and often
underutilized IP networking infrastructure to provide localized processing, speedy information
access, and remote data replication.
SYMMETRIX SYMMETRIX
SRDF/FC
SRDF/FC
CONNECTRIX
The GUI screens of EMC ControlCenter provide easy point-and-click monitoring and control of
SRDF environments, as well as planning, monitoring, and managing other EMC hardware and
software functions plus those from third parties which are compliant.
SRDF and Symmetrix The unique capabilities of SRDF enhance the already impressive information protection and
availability capabilities of EMC’s Symmetrix enterprise storage system. Standard Symmetrix
protection features include:
• Full-system battery backup
• Redundant disk and channel directors
• A choice of RAID protection levels
— Mirroring, EMC’s RAID 1 protection
— RAID-S, EMC’s enhanced parity-based protection
• Fully non-disruptive microcode loads
• Non-disruptive component replacement
• Dynamic disk sparing
• Automatic cache and disk scrubbing
• Integrated Remote Maintenance Processor (RMP) with automatic “phone home” capability

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Chapter 2
SRDF Uses and Applications
Overview As businesses become more global, applications grow significantly larger. A superior information
protection solution, one that provides not just data safekeeping and disaster recovery capabilities,
but also business continuity and acceleration is a necessity.
To address this need, companies and government agencies are increasingly implementing solutions
based on remote mirroring technologies. Remote mirroring is capable of making data available in
less than an hour in the case of a disaster (versus typical tape recoveries of 24 to 72 hours), and with
data current as of the last completed transaction.
Remote mirroring reduces the time, costs, and data recovery efforts associated with traditional
disaster recovery methods. System restoration times are minimized and data loss prevented so that
data is recovered at the exact point of failure and in an expedient manner. Users gain the ability to
continue their business operations in the event of planned outages such as daily backups, scheduled
maintenance, and data center migrations or consolidations. The financial impact of
both unplanned and planned events and their severe business disruption can be minimized or
negated altogether.
EMC’s Symmetrix Remote Data Facility, SRDF, accomplishes remote mirroring by connecting
intelligent storage systems that reside locally or thousands of miles apart, independently of host
processors. Introduced in 1994, SRDF is the leader in its market with thousands of licenses
installed worldwide. With the recent additions of Fibre Channel connectivity, Virtual Private
Networks using the Internet Protocol (IP) to traditional SRDF, EMC also expands your
opportunities for business acceleration.
Disaster Recovery, When a disaster occurs and the decision is made to utilize a disaster recovery site, many activities
The Old Way must take place. The recovery site must be accessed and networks and telephones must be switched
to the new site. The most recent tape copies of the operating systems, libraries, databases, and
catalogs from the off-site vault must be retrieved and transported to the recovery site. And finally,
the tape copies must be restored to disk, which may take days. This is not the most expedient
method, but is the most widely used practice in the world today. Any method that shortens this
cycle is obviously of great interest to disaster recovery planners.
Disaster Scenarios Disasters may occur for any number of natural or man-made causes. Protection is required to
recover from earthquakes, floods, fires, hurricanes, protracted power outages, destruction of the
primary processing facility by terrorist activity, or any of hundreds of other causes including
database corruptions and programming failures.
SRDF and EMC TimeFinder SRDF functionality can be combined with that of EMC TimeFinder to create expanded
capabilities. EMC TimeFinder is used to create locally resident, point-in-time, mirrored copies of
active volumes called “Business Continuance Volumes” or BCVs. While production applications
continue to perform at full capability and capacity, BCVs can be used for other business purposes.
For example: application testing with real data, on-demand data warehouse loads and refreshes, or
running batch processes, such as backups.
With SRDF installed, the BCVs can be created at either local (source), remote (target), or both
types of Symmetrix sites. SRDF maintains full disaster recovery/business continuity even as these
other operations proceed, ensuring information availability and simultaneously working with
TimeFinder to enhance enterprise productivity and business acceleration.
SRDF and Symmetrix systems can support AS/400 systems with the full suite of Symmetrix features and
AS/400 Environments benefits. EMC CopyPoint enabling software that runs on AS/400 systems and affords Information
Protection to data on EMC-connected Symmetrix.
When used with SRDF, CopyPoint reduces nonproductive AS/400 system time to a minimum
by allowing a second AS/400 the ability to offload many operational requirements such as
point-in-time backups, batch processing, report generation, application testing, and data
warehouse loading. Contact your EMC representative for complete details on the use of SRDF in
AS/400 environments.
ESCON
IP
Symmetrix (A) Symmetrix (B) Symmetrix (C)
FC/AL
Point to Point ESCON

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In the above scenario, it will have taken at least 18 hours to get the environment prepared to where
it was before the disaster. Missing information and data, with consequent business risk, is
the potential result of this scenario. Outages of this duration will clearly be intolerable in the
new E-economy.
Create the Tape Copies The time taken for retrieval and transport can be eliminated by actually writing the tapes at the
at the Recovery Site recovery site using channel extenders and tape silo facilities. This clearly delivers an advantage in
that the retrieval and transport of the tapes at the time of disaster is eliminated. However, the tapes
must still be restored to disk, which is the most time consuming activity in the recovery process.
The latencies associated with tape-based recoveries are simply too long.
Data Copies on Disk Advances in channel extender facilities ó whether SCSI, ESCON, IP, or Fibre Channel — and
host/server communications have facilitated keeping two copies of data available on disk in
real-time mode.
Using the Host/Server One method involves using the host/server to write data to both local and remote disk. This raises
to Create the Copies several issues of resource consumption, currency of data (Is the data real-time or copied to disk at
specific moments in the daily cycle?) and performance impact on daily operations, as well as
implications on application maintenance if the copy facility is embedded in user programs.
Another technique involves the host/server transmission of transactions as they occur. This second
capability gives the user the option of storing the transactions on remote disk for later, relatively
rapid, application to a copy of the database environment, or of direct application. In either event,
CPU resources are still utilized and performance impact and cost issues are significant.
Disaster Recovery Testing Typical disaster recovery testing involves manually intensive recovery drills, complex procedures,
and business interruptions. In contrast, with SRDF IS staff can simply switch to the remote site at
any time. Testing can be performed during normal business operations, a significant time and
cost-saving option. For businesses serving global markets that operate on a 24 x 7 x 365 schedule,
ensuring the highest level of data availability with no downtime is especially critical.
Business Continuity Major impediments to business continuity exist that are mundane in nature and considered normal
business and operational practices. These involve outages from nightly backups, new application
testing, database loads and refreshes, and hardware and software upgrades. However, in today’s
highly competitive and often global environments, businesses can ill afford the loss of productivity
that is associated with these outages. Fortunately, with SRDF, such outages are no longer necessary.
Business continuity planning must deal with all the challenges to system availability. Plans and
processes must be put in place to:
• Backup data without shutting down enterprise systems
• Nondisruptively make duplicate copies of databases as required
• Nondisruptively load data warehouses as frequently as required
• Accomplish application upgrades without shutting down those applications
Disaster Recovery Sites The disaster recovery plan must ensure that an alternative site is identified which meets the
planner’s requirements with respect to:
• Distance from the primary site
• Communications capability
• Processing power
• Storage capacity
• Accessibility for the required personnel
Depending on the nature of the expected events that would cause a disaster, the site may be within
yards of the primary site or separated by hundreds of miles. In the case of a fire, a recovery
environment behind a firewall in the same building may suffice. In the event of an earthquake, a
whole region may be devastated. Defining and verifying the physical site is a relatively easy process.
Investigation and negotiation ensure that the required infrastructure is in an appropriate place and
sufficient for the task.
Traditional Techniques Various techniques have evolved for protecting information from natural and unnatural disasters.
for Data Recovery Several of the more prominent are listed here.
Store the Tape Copies It is a normal part of day-to-day operations in most data processing facilities to take backup copies
at a Secure Site of critical data, libraries, and databases to enable ‘rapid’ restoration in the event of a problem.
Typically, two copies are made, one stored on-site and the second stored off-site in a secure facility.
Copies of data, generally on tape reels or cartridges, are usually stored in a secure facility, offsite
from the primary processing facility. The tape cartridges are produced, typically overnight, and
transported to the storage facility. This process alone introduces significant time delays in the
currency of any backup data. The tape copy may have gone through a cycle similar to that below:
• Database quiesced at midnight
• Copy taken (4 to 6 hours)
• Tapes stacked for shipment to secure site
• Transport calls at 10:00 a.m.
• Tapes driven to secure site
• Tapes are secured at noon
Thus the tape copy that is stored at the secure site may be several hours old (12 in the above
example), and represents the current best starting point for recovery in the event of a disaster.
When required, the tapes must be retrieved and transported to the recovery site. This generally
means delays of many hours for the following functions to occur:
• Select the appropriate recovery tapes from the secure site (2 to 4 hours)
• Transport to the disaster recovery site (2 to 4 hours)
• Restore to disk (8 to 18 hours)
• Roll forward databases to best recovery level (6 to 12 hours)
• Resume application processing

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Clearly, the implication is an extended application outage, often as much as 20 or 30 hours or
more. As the cost of application downtime grows, the financial impact of such a move can be
considerable. SRDF reduces the size of the outage taken for the switch to the new data center to less
than an hour by:
• Remotely mirroring the application data and libraries beginning days or weeks prior to the move
and keeping the local and remote copies synchronized with minimal performance impact
• Performing data validations at the new center prior to the cutover, while applications are still
running at the original site
• Running the applications until the moment of cutover
• Shutting down the application in the old site
• Restarting the applications at the new site
Workload Migrations The fundamental consideration for workload migrations is minimizing the outage taken by an
application as its data is moved to the host/server where processing is to occur. Reasons for moving
workloads include:
• A different host/server is better suited to running the application
• Application competency is superior in a different location
• Merger and acquisition activity at the corporate level calls for the least disruptive absorption of a
workload by an existing facility
SRDF provides the means to support these activities without disrupting normal operations
AS/400 Applications As with any mission- or business-critical application, customers using AS/400s require higher levels
of data protection than in less sensitive environments. SRDF can provide that extra level of
protection with no additional operational management or host system overhead. These critical
environments need to conserve all the precious production time they can. EMC CopyPoint
provides AS/400 customers a way to protect vital resources and extend the production day
while still completing necessary data backups, batch processing, etc., without consuming any
system overhead.
EMC’s CopyPoint software gives AS/400 enterprises the ability to significantly enhance their
operational productivity while also achieving strengthened protection against outages.
SRDF LINK
Recovery
Target Symmetrix
Primary
Source Symmetrix
Eliminating the Standard information management practice is to conduct regularly scheduled information
“Race to Sunrise” backups. With today’s global enterprises, this practice has become anything but routine.
Applications have grown larger, backup windows have grown smaller, and any downtime results
in potential revenue loss. SRDF eliminates the race to sunrise while allowing business operations to
run continuously. Scheduled backup operations or new application testing is performed from the
target Symmetrix data while normal operations are continuously running on the source
Symmetrix. All the while, information is safely protected, available, and expanding its earning
power. For many businesses, the SRDF payback is measured in just days.
Loading Data Warehouses All too often conventional data warehouse loads and refreshes occur infrequently, when no other
business-critical functions are in process. SRDF rectifies this situation and gives analysts and
management personnel access to the latest information from which to plan business strategies and
take advantage of immediate opportunities. Using SRDF remote copy volumes, data warehouses
can be loaded and refreshed at more frequent intervals while normal operations to support the
enterprise proceed nondisruptively.
Scheduled Maintenance SRDF enables business operations to continue during scheduled site maintenance, such as
operating system upgrades, host/server upgrades, and environmental disruptions. After
applications are switched to a remote site, normal operations continue using the remote copy of
synchronized application data.
Data Center Migrations Data center migrations occur for many reasons, including:
• Moving to a new building
• Company move to a new site
• As a result of a corporate reorganization
• As a result of a corporate merger or acquisition
From a data point of view, the migration involves:
• Identifying a specific time for the move, typically the least busy time on a low-activity weekend
• Shutting down applications
• Copying all data and libraries to tapes
• Transporting either the disk or tape copies to the new location
• Installing the disk or restoring the tapes
• Executing appropriate data validation processes, if required or desired by the user
• Resuming applications

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Chapter 3
SRDF Detailed Description
SRDF Principles At the simplest conceptual level, SRDF is mirroring (RAID level 1) of one disk device (source) to a
of Operation second device (target) in a physically separate Symmetrix system over ESCON or other high-speed
communication links. The distance separating the two Symmetrix systems can vary from within
the same room to thousands of miles.
As with RAID 1, if either disk in the mirrored pair fails, the requested data is instantly available
from its mirror copy. No disruption to normal operations occurs. Once the disk again becomes
available (through repair, replacement, or operational procedure), the newly available member of
the pair can be resynchronized with its mate.
Because the mirrored volumes reside on separate Symmetrix systems, unique capabilities result
over and above the information protection features of a remotely mirrored RAID 1 system. The
duplicate volumes can be temporarily disconnected from the mirroring scheme and used
for nondisruptive:
• Backup and restore operations
• Development and testing of applications from third-party software providers
• Timely loads and refreshes of data warehouses and data marts
• Complex queries and report generation
• Disaster recovery testing
SRDF Hardware SRDF requires a minimum of two Symmetrix systems — one source system and one target system.
Components Additionally, there may be one server system sending information to multiple target systems and/or
multiple sources sending information to one target. SRDF requires a minimum of two Remote
Link Directors (RLDs) or Remote Fibre Directors (RFDs) to be installed in the Symmetrix systems,
both source and target. The Remote Link Director is a two-port channel adapter, microcode-
configured as the link between the Symmetrix systems. Symmetrix supports up to eight RLDs
depending on the Symmetrix model in use and the business continuity requirements. Remote Fiber
Directors are two-port channel adapters, again installed in pairs for redundancy on both
Symmetrix systems. The maximum number of RFDs varies by Symmetrix model. The following
figures schematically illustrate typical Symmetrix SRDF connectivity.
Hardware component usage between two Symmetrix units in a uni-directional configuration
CD CDCACHE RLD
DD DD RLD
S1 S3 S5 S7
S2 S4 S6 S8
RA1
SYMMETRIX A
CD CD CACHERLD
DD DDRLD
T1 T3 T5 T7
T2 T4 T6 T8
RA2
SYMMETRIX B
RA1
RA2
At the time of a backup, the production AS/400 (source) application is quiesced and the AS/400
main storage is flushed to clear all active data from the AS/400 memory. SRDF remote mirroring at
the destination (target) Symmetrix partition is suspended. The entire quiesce/flush/suspend process
takes just a few minutes. Then the production AS/400 can continue its production applications.
With the SRDF link suspended, the backup, using CopyPoint, can commence from the second
AS/400. Because Symmetrix offers protection for the source data, full business continuity is
maintained even while SRDF mirroring is suspended.
Once the backup is completed, SRDF mirroring is restored, and the source and target data volumes
are automatically resynchronized by the Symmetrix with no AS/400 system overhead.
Growing Your SRDF over IP presents new opportunities for growth by capitalizing on e-focused business trends.
Business with SRDF Take advantage of SRDF’s remote mirroring capabilities to replicate data such as mail system
indexes and mail boxes, establish application test beds, deliver widespread management reports
and distribute software. The lower telecommunications costs of IP-based SRDF can be reinvested
to make wider or growing data more accessible, increasing the volume of data that is remotely
protected, and optimizing localized applications or data.
SRDF Over IP Optimizes Carried over IP, data is a replicated mirror, using delayed synchronization techniques. Applications
Information Deployment for which this delayed synchronization are appropriate include data warehousing, development
systems, mirrored web sites, multi-hop, bulk data movement, and data center consolidation.
SRDF over IP lets you accelerate, simplify, and optimize your business-critical information
processes and resources in innovative, cost-effective ways. For example, if you need to deploy
mirrored Web sites, refresh data warehouses or migrate applications and databases, SRDF Over IP
can create copies of the data and transmit them over IP-based Virtual Private Network to a remote
Symmetrix system.
Using an IP network for data replication can significantly lower operational costs, since an IP
communications infrastructure likely exists. Other uses for SRDF’s mirroring capabilities using the
IP network might include replicating mail system indexes and mail boxes to establish application
test beds, deliver widespread management reports, and software distribution.
SRDF Over Fibre Channel Applications that would particularly benefit from a SRDF FC topology are those that require
Increases Throughput synchronous, realtime mirroring. Information for financial transactions, such as for brokerage
accounts, banking, and mortgage servicing, and critical production data such as for
telecommunications, databases, and manufacturing systems are obvious examples of applications
that would benefit from SRDF over FC. High bandwidth, efficiency, low delays, and low overhead
are familiar advantages of FC. In campus mode, within 10 kilometers, SRDF over FC will run
synchronously, with significantly added throughput over traditional connection methods.

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Dramatic throughput increases are possible when SRDF runs across Fibre Channel networks.
SRDF Implementation EMC Professional Services are available to help you receive optimum value from your
implementation of SRDF. Specific planning and design services tailor your SRDF solution to your
particular enterprise business continuity requirements.
SRDF implementation and maintenance is both easy and cost-effective. No special application
coding is required and no CPU overhead is incurred. SRDF functions completely independently
from the host processor and operating system. As a result, all major mainframe and open systems
hardware and software platforms are supported.
SRDF setup and installation parameters are accomplished through the Symmetrix integrated
service processor. Optional EMC ControlCenter software may be used to configure and manage
SRDF implementations by means of an easy-to-use GUI or via a command line interface
for automation.
An SRDF implementation involves the following components:
• A minimum of two Symmetrix enterprise storage systems. In the case of SRDF over IP or FC, must
be specific models of Symmetrix 3000, 5000, or 8000 series.
• Symmetrix Enterprise Storage Platform (ESP) software (required for installations with a mix of
Symmetrix 3000 and 5000 systems).
• Remote Link Adapters (RLAs) or Remote Fiber Directors (RFDs).
• Microcode license for SRDF for each Symmetrix.
• Communication links between Symmetrix systems.
• For use with the IP protocol, a channel extender must be used on each end.
SYMMETRIX SYMMETRIX
SRDF/FC
Multi-hop, an SRDF Extended Distance solution, involves three Symmetrix systems. For more
information on this solution, please see page 23.
SRDF can run over Virtual Private Networks with addition of partner-supplied hardware that
encapsulates SRDF traffic and makes it ready for transmission via IP.
UNIX Server
Symmetrix Symmetrix
Router Router
SCSI
FC-AL
IP-BASED
Network
MVS Host
ESCON
server
264
SRDF/
ESCON
CNT
USED
Adding
IP
Suport
to T3/E3 and
ATM
CNT
USED
SRDF/
ESCON
CD CD
DD DD
T1 T2 S1 S2
SYMMETRIX A
CD CDRLD
DD DD
T1 T3 T4 S2
T2 S1 T5 S3
RA2
SYMMETRIX C
RA1
RA2
RA1
CD CD
DD DD
S3 T3 T4 T5
SYMMETRIX B
RA1RA1
CACHE
RLD RLD RLD
RA2 RA2
RLD RLD RLD
RLD

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Multihost Support
Vendor System Minimum
Operating System
Bull®
Escala AIX 4.2.1, varies by model
Compaq®
/DEC®
AlphaStation and AlphaServer Digital®
UNIX®
V3.2A,
Series 3000 AXP, Models 300-900, OpenVMS®
6.2 or higher,
1000, 2000, 2100, 4100/4200, Windows NT V3.5.1
8200, and 8400
Data General®
Aviion®
5500 (88K-based), DG/UX®
R4.11 MU03
4900/5000 (Intel-based)
Data General®
AV4900, AV5900 (Pentium®
) Windows NT®
V4.0
HP®
3000-900 Series MPE/ix 5.0
HP 9000/700 Series: 725/100, 735/99, HP-UX®
9.05,
735/125, 755/99, 755/125, HP-UX 10.20
715/100XC, C-Series, J-200, J-210,
210CX, 250
HP 9000/800 Series: E, F, G, H, I, HP-UX 9.04, 10.20 varies by model
T500, D, K
IBM AS/400®
(all 9406 including RISC, OS/400®
V3R2
except Model B)
IBM RS/6000™
AIX®
4.2.1
IBM SP2®
AIX 4.2.1
IBM S/390®
& S/370™
Any
IBM Symmetry®
2000 & 5000 DYNIX/ptx®
2.1.5
IBM NUMA-Q DYNIX/ptx®
4.3
Intel®
-Based All Novell®
3.12,
Servers Windows NT 3.5,
or OS/2®
2.1
NCR®
34xx, 35xx, 36xx, 41xx, 45xx, UNIX SVR4 2.03.01
3600AP, 5100 (S, C, M)
Siemens®
-Pyramid Nile®
Series Datacenter®
OSx 94D079.6
RM 1000 Datacenter OSx 95M079
Reliant UNIX V5.43C0053
Silicon Graphics®
Challenge®
S, L, DM, & XL IRIX®
5.3
Silicon Graphics Origin 200 and 2000 IRIX 6.4.1
Stratus Continuum 400 Series HP-UX B.10.20.1
Sun®
SPARCserver and SPARCcenter 10, SunOs®
4.1.3,
20, 1000, 2000
Solaris 2.3
Sun UltraSPARC Workstations and Solaris 2.5.1
UltraSPARC Servers
Unisys®
Clearpath IX, NX OS/MCP, OS/2200
Note: Contact your local EMC sales representative for specific hardware and software
configurations.
In addition to a wide range of platform support, SRDF is configurable into multiple Symmetrix
environments such that one Symmetrix serving as an SRDF target system can support up to 16
other Symmetrix systems serving as source systems. Generally the number is less than 16 as this
would necessitate a physical disconnection of one Symmetrix from the remote link adapters in
order to gain access to a server processor to resume business operations.
Installation and Planning Several configuration guidelines must be met in order to ensure SRDF properly executes in a
specific environment. Successful implementation of SRDF involves choosing the appropriate
features that meet the business continuity/disaster recovery and performance needs of
the enterprise.
The following aspects should be considered when choosing the types of data and volumes to be
remotely mirrored:
• Databases, logs, catalogs, system residence volumes, and program libraries are excellent candidates
for SRDF mirroring.
• Page, spool, and work datasets are poor SRDF candidates as they are easily recreated on the
target location.
Every SRDF installation is unique and therefore it is important to thoroughly discuss the business,
configuration, and application performance requirements with an EMC representative.
Supported Environments Since SRDF runs on Symmetrix, it is operating system independent. Thus, any host environment to
which a Symmetrix system is attached is supported. The following chart lists the currently
supported host hardware and operating system platforms. Consult EMC for updates to the list.

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SRDF Extended Extended Distance solutions are appropriate for wide area protection and for areas where fiber
Distance Solutions cannot be installed; for example, where data centers are further than 66 kilometers apart or local
restrictions will not allow the placement of fiber. Extended Distance solutions can also be used to
link data centers to a centralized private recovery site or any of several commercial regional
disaster recovery service providers.
In Extended Distance solutions, the RLA’s output is still to ESCON fiber. This ESCON fiber is
connected to a telecommunications protocol conversion unit, which is provided by any of several
independent vendors. These network boxes convert the ESCON protocol to the appropriate
telecommunications protocol, whether T3/T1, E3/E1, or ATM. Network boxes available from
Computer Network Technology, InRange Technologyís GEN, StorageTek (formerly NSG), and
Computerm Corporation are currently supported. Some feature data compression. For further
information, contact the independent vendors directly.
SRDF FarPoint SRDF FarPoint is a high performance feature that optimizes both the long distance (>15 km)
Campus and Extended Distance solutions. SRDF FarPoint significantly increases performance by
eliminating queuing and increasing communication line utilization. This results in a more cost-
effective solution and, in some instances, allows the same level of performance with fewer lines. For
more detail on SRDF FarPoint, see “SRDF FarPoint Operations” later in this chapter.
SRDF Multi-hop Capability Another time- and cost-saving Extended Distance offering is SRDF’s multi-hop capability. Multi-
hop enables SRDF users to mirror only data that has changed since the last update to a Symmetrix
system in a third location. Symmetrix to Symmetrix transmissions are made synchronously in the
local or campus area, whereas delayed synchronization modes are used for long-distance segments.
Utilizing EMC TimeFinder, this capability is ideal for cost-effectively mirroring data long-distance.
By copying only the changed tracks, less bandwidth is consumed, performance is enhanced, and
transmission times are shorter. Multi-hop mirroring to the third site can take place during off-peak
times or over lower cost transmission lines or via IP-based Virtual Private Networks. Recurrent
monthly line costs can be dramatically reduced, quickly recouping the investment in a third
Symmetrix system.
SRDF’s multi-hop capability decreases line transmission costs by mirroring only the tracks changed
since the last update and taking advantage of lower cost transmission lines or IP-based VPNs.
Symmetrix Source
Synchronous
Mode
Los Angeles Phoenix New York
Adaptive
Copy Mode
Using FarPoint
Intermediate
Symmetrix Target
Final
Symmetrix Target
SRDF Campus Solution In the Campus solution, the Symmetrix systems are connected with ESCON fiber from as little as
3 meters to 66 kilometers. For distances between 0 and 3 kilometers, no converters or repeaters are
needed with multimode fiber connected directly to the Remote Link Adapters (RLAs). If the sites
are more than 3 kilometers apart, then standard ESCON channel directors, repeaters, and
converters must be used in 20-kilometer segments.
SRDF over Fibre Channel will run synchronously in campus mode up to 10 kilometers, from the
host Symmetrix to the target Symmetrix or Connectrix switch if in the middle.
An EMC 9191 device is used to:
• Support multimode-to-singlemode conversion and singlemode-to-singlemode signal regeneration.
• Support SRDF at full ESCON speed.
• Support source and target Symmetrix systems located at distances between 3 and 26 kilometers.
For customers who require greater distances, three EMC 9191 devices can be used to extend the
path up to 66 kilometers.
The Campus solution supports all SRDF modes of operation and bi-directional SRDF capability.
Bi-directional SRDF capability means that both source and target Symmetrix systems can act as
both source and target for each other. This is particularly useful when the sites are to be used for
backup sites as well as for other applications. Dual mode, a variant on Bi-Directional mode, is
also supported.
SYMMETRIX
SOURCE H
SYMMETRIX
SOURCE E
SYMMETRIX
SOURCE G
SYMMETRIX
SOURCE F
SYMMETRIX
SOURCE D
SYMMETRIX
SOURCE C
SYMMETRIX
SOURCE B
SYMMETRIX
SOURCE A
SYMMETRIX
TARGET

SRDF over IP for SRDF over IP takes advantage of two fundamental characteristics of IP-based VPN networks.
Extended Distances VPNs are often underutilized and they do not require a dedicated circuit. This latter point means
that operational telecommunications costs (usually priced on a per circuit mile basis) can be
dramatically reduced.
SRDF Modes of Operation SRDF offers flexibility in specifying how data transfer is performed between source and target
volumes. The following modes of operation and configuration options can be intermixed and
operate simultaneously in the appropriate manner in order to achieve a proper balance among
performance, communication link cost-effectiveness, and timeliness of information
synchronization required.
Primary mode choices are:
• Synchronous Mode
• Semi-synchronous Mode
A Secondary mode is:
• Adaptive Copy Mode
Each logical volume must be configured in one of the two primary modes. The decision on which
primary mode to select is based upon such factors as performance and distance.
In addition, there are several configuration options that can be specified for Symmetrix volumes.
These are:
• Consistency Group Utility for MVS
• Consistency Group Feature for Open Systems
• Domino Option
• SRDF FarPoint
• Invalid Tracks
Synchronous Mode Synchronous Mode is most appropriate for data that must be written in two locations before the
application is to continue. This ensures that a second copy of the data, accurate up to the last
transaction, is immediately available for use. Synchronous Mode provides mirroring of data
between the source Symmetrix and the target Symmetrix system. In this mode, data is first written
to the source system and then to the target system. Next the application is notified that the I/O is
complete. AS/400 systems are supported only in Synchronous Mode.
When writing to a remotely mirrored volume, the following sequence of events takes place in Syn-
chronous Mode:
Step 1: Data is written to the cache of the local Symmetrix and an entry is placed in the
SRDF FIFO (First In, First Out) queue for the updated data.
Step 2: The first available RLA takes the first entry in the queue and moves it across the
link to the remote Symmetrix cache.
25
24
Step 3: The remote Symmetrix acknowledges the receipt of the data.
Step 4: The I/O complete signal is presented back to the host/server, which initiated the I/O
request.
In Synchronous Mode, SRDF writes data simultaneously to the cache of both source and target
volumes, in real time, before the I/O is complete. SRDF over Fibre Channel is used in local and
campus configurations and may optionally connect through the Connectrix family switches in
pass-through mode.
Semi-Synchronous Mode Semi-synchronous operation is used to mask any performance impact that could result from I/O
propagation delays. Semi-synchronous Mode writes data to the source system, completes the I/O,
and then synchronizes the data with the target system. Since the I/O is completed prior to
synchronizing data with the target system, this mode provides an added performance advantage. A
second write will not be accepted on a volume until the target has been synchronized (hence,
not asynchronous).
By presenting an earlier I/O complete signal to the host/server, the host/server can continue
processing reads to the logical volume. Most applications do a read before they do a write. This
implementation successfully masks the I/O elongation that is created by the propagation delay to
the target system in a pure synchronous mode.
When writing to a remotely mirrored volume, the following sequence of events takes place in
Semi-synchronous Mode:
Step 1: Data is written to the cache of the local Symmetrix and an entry is placed in the
SRDF FIFO queue for the updated data.
Step 2: An I/O complete signal is presented back to the host that initiated the request.
Step 3: The first available RLA takes the first entry in the queue and moves it across the
link to the remote Symmetrix cache.
Step 4: The remote Symmetrix acknowledges the receipt of the data.
CD CD
CPU A
RLD
CACHE
RLD
CD CD
CPU B
RLD
CACHE
RLD
1 4
3
2
SYMMETRIX CONTAINING
SOURCE (R1) VOLUME
TARGET (R2) VOLUME

27
26
Domino Option By specifying the Domino option for the mirrored pair, any failure to complete write operations to
both volumes in the relationship will cause the source volume to present an ‘intervention required’
status to the operating system. This in turn makes its way back to the driving application and alerts
the user to the fact that the mirrored write did not complete and gives the user the option of
preventing further activity.
SRDF FarPoint Option SRDF FarPoint significantly enhances Synchronous Mode performance for SRDF Extended
Distance solutions. SRDF FarPoint allows I/O from multiple logical volumes to be serially
transmitted on the SRDF link by a single Remote Link Director (RLD), up to one outstanding I/O
per logical volume. This enables the SRDF communication link to be more fully utilized depending
on the distribution of application I/O write activity across multiple logical volumes. If an
acknowledgement is not received from the distant end, SRDF FarPoint will resend data for that
element and all that follow in the pipeline.
The major advantages of using SRDF FarPoint for Extended Distance solutions are twofold:
• Bandwidth utilization is improved at long distances because there can be multiple I/Os serially
transmitted by an additional RLD at any time. Thus, as line distance increases, this results in better
utilization of line bandwidth.
• The SRDF I/O write operation will spend less time waiting in the queue to be serviced, resulting in
higher I/O performance and lower average response times.
SRDF FarPoint is available for Extended Distance implementations and Campus implementations
greater than 15 km.
Invalid Tracks Attribute The Invalid Tracks attribute is implemented at the logical volume level. This prevents a target
volume from becoming ready when it is not fully synchronized with its source.
SRDF Management SRDF can be managed:
• Through the Symmetrix service processor (EMC service personnel only).
• Through EMC ControlCenter, SRDF/TimeFinder Manager option.
EMC ControlCenter is an optional software product that offers unparalleled ease-of-use in
implementing, reconfiguring, monitoring, and terminating SRDF configurations. With EMC
ControlCenter SRDF users can perform such functions as:
• Query the status of the SRDF relationships (drives, links)
• Modify the options for each logical drive pair (Synchronous, Semi-synchronous, Adaptive Copy,
Invalid Tracks)
• Issue SUSPEND or RESUME commands for mirroring activity for individual drive pairs or entire
SRDF subsystems.
A comprehensive list of the SRDF commands and their functions may be found in the appropriate
technical documentation.
In Semi-synchronous Mode, SRDF writes data to the source system, completes the I/O, and then
resynchronizes with the target system.
Adaptive Copy Mode The Adaptive Copy Mode of operation is useful for data center migrations or for migrating large
blocks of data from one place to another or when using SRDF over IP. When choosing this mode of
synchronization, the user should be aware that data is not transferred in a serialized manner.
Therefore, Adaptive Copy Mode is not a prime choice for real-time recovery.
In Adaptive Copy Mode, the user specifies that a source volume’s primary mode of operation be
suspended. Data is transferred from the source volumes to the remote volumes without waiting for
an acknowledgment and allows a lag between source and target volume of a specified number of
I/Os. This allows SRDF to manage the Adaptive Copy volumes at a lower priority, thus enabling
applications using that volume not to encounter propagation delays while data is transferred to the
remote site.
If the number of I/Os at which the threshold is set should exceed the specified number, SRDF
suspends its asynchronous state and reverts back to its primary mode of operation until the
number of unsynchronized I/Os are below the threshold. When the I/O threshold is re-established,
SRDF reverts to Adaptive Copy Mode again for the pair.
Consistency Groups In MVS and open systems environments, SRDF users also have the option of using the Consistency
Groups to provide database coherency protection for volumes spread across multiple Symmetrix
systems. The Consistency Group capability, available with latest microcode versions, maintains
database coherency across an SRDF configuration by monitoring data propagation from the
source devices (R1) in a defined consistency group to their corresponding target (R2) devices.
If data from one or more source devices in a Consistency Group cannot reach their corresponding
target devices, it suspends all data flow to the consistency group’s target. This ensures that a
consistent database — up to the point in time of data propagation failure — exists on the remote
side of the configuration for use by applications.
I/O to the local Consistency Group devices can still occur while data flow to the targets is halted.
Although these updates are not immediately sent to the remote site, they are propagated through
usual SRDF operation once the affected CG links are again operational.
CD CD
CPU A
RLD
CACHE
RLD
CD CD
CPU B
RLD
CACHE
RLD
1 2
4
3
SOURCE (R1) VOLUME
TARGET (R2) VOLUME

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Example of source/target switching
Source Control of Target SRDF commands can be performed at target locations without a host being present. Point-in-time
backups and disaster recovery testing at the target site can be remotely managed from the source or
production site. The primary source site can also create the Business Continuance Volume (BCV)
that serves as the source for mirroring to a third location in a multi-hop solution. In addition,
TimeFinder commands can be executed over SRDF links.
HP MetroCluster Hewlett-Packard’s MC/ServiceGuard with MetroCluster software and EMC SRDF is an
integrated, open systems disaster-tolerant solution enabling geographically dispersed HP-UX
clusters to be combined into a single, manageable system with automatic failover of applications.
When a site becomes inoperable due to a system failure or a disaster event, application package
switching occurs. This action automatically transfers control of the affected application to another
HP 9000 system located in a secondary site, while also automatically read/write-enabling remotely
mirrored EMC disk devices associated with the transferred application.
HP MetroCluster for EMC SRDF allows cluster support between sites up to 40 kilometers with an
intersite link, which is used to provide heartbeat communication between cluster nodes. HP
Continental Clusters extend the distance limits while operating in a similar manner.
SRDF Source SRDF Target
R1 R1 R2 R2
Without R1/R2 Swapping
SRDF Source SRDF Target
R1 R2 R1 R2
With R1/R2 Swapping
Chapter 4
SRDF Usability Considerations
SRDF Features SRDF features provide users with unsurpassed information protection capabilities — capabilities
and Capabilities that not only protect vital information assets, but also enable users to put those assets to
competitive advantage. This chapter describes many of these features and capabilities as well as
how SRDF employs them in typical scenarios.
Sequential Data Updates When using Synchronous or Semi-synchronous mode, updates occur sequentially across the SRDF
Across the Link communication links. When a WRITE to an SRDF-participant volume takes place from a host, the
data is moved into the cache of the local controller. SRDF maintains a queue, called the SRDF
queue. This queue contains pointers to data which has been written to the local cache and that must
be moved to the remote Symmetrix. Entries are made to this queue as the data arrives from the host.
The data is moved from the queue in FIFO fashion, ensuring that data sequencing is preserved as
data is moved between the SRDF participants.
Local and Remote Mirrors With SRDF the user may have two, three, or four copies of the same volume in combinations of
of the Same Volume mirroring or BCV volumes. This high availability capability enables flexible solutions such as
point-in-time backup of data.
SRDF and RAID-S SRDF fully supports the RAID-S capability of EMC Symmetrix systems. RAID-S is EMC’s
Compatibility exclusive high performance parity-based RAID protection scheme. RAID-S protection can be
intermixed with EMC Mirroring (RAID 1) or non-RAID-protected volumes in an SRDF
environment, both locally and remotely.
Dynamic Sparing Symmetrix Dynamic Sparing capability can be used to provide protection for SRDF mirrored
drives. Dynamic Sparing can be used:
• To augment the protection provided by local and remote mirrors by providing yet another level of
safety in the event of a volume failure. In this combination, the already impressive availability
profile afforded by optional full local and remote mirrors (four addressable copies of data!) is even
more so.
• As a less costly manner of providing protection, but with the realization that dynamic sparing alone
may not provide full protection in all circumstances.
Source/Target Switching This capability enables reconfiguration of synchronized SRDF volumes causing R1s (the source) to
become R2s (the target) and R2s to become R1s. It results in a reversal of the data flow
and facilitates continual disaster recovery readiness during workload migrations. Specific
benefits include:
• Swapping of specific host/server applications may be remotely mirrored, providing continued
disaster recovery readiness in the event of either site going offline after an R1/R2 swap.
• Allows host/server hardware and/or operating system upgrades without compromising disaster
recovery readiness by continuing to make the data available with R1/R2 swapping.
• Eliminates the need to perform SRDF source site resynchronization because remote mirroring will
continue between the swapped SRDF sites (assuming the SRDF source site is online).
Note: Contact your EMC representative for a list of platforms supported for Source/Target
Switching.

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Potential Events The balance of the chapter discusses typical “what if” scenarios and how SRDF manages them.
Local or Remote Volumes If the user has implemented local as well as remote mirrors for the volume, then most types of
“Out of Service” events are quite transparent to the user.
If the drive that failed is not locally protected, the application will continue, utilizing the RAID-1
capability of SRDF. Applications continue by reading data from and writing to the survivor in
the pair. When repair is effected nondisruptively, automatic resynchronization of the drives
takes place.
Link Breaks When one or more SRDF links break, applications continue running, but performance will likely
be impacted because all I/O activity is then routed across the remaining links.
If all links break, the Domino option may be invoked, which will prevent applications from
running against the local Symmetrix. If this loss of availability is not desirable, Consistency
Groups for MVS or open systems can be utilized to ensure integrity on the remote side while
maintaining application availability at the local site. Upon link resumption, the changes that
occurred on source volumes can be copied automatically to the target volumes, while normal
application I/O activity continues.
Return to Source Site If after processing at the recovery site, as a result of a disaster or a test, you wish to return to the
primary site, you can do so regardless of whether the original or new equipment is in place. Restart
processing begins almost immediately.
The following steps are required:
• Link the Symmetrix devices together in the originally defined configuration
• Restore target volumes to the source volumes
• Restart applications on the source side
It is not necessary to have full resynchronization before starting applications. This is because
SRDF knows where valid data resides. As the application processes data, it will be pre-emptively
moved from the target to the source if it is requested prior to having been moved. While processing
is in progress, SRDF can resynchronize all the data from the target volumes to the source devices.
Returning to “normal” operations is accomplished with almost as little pain as recovering from
the disaster using SRDF flexibility.
Or, you can switch the roles of source and target, as described on page [layout assigns page] of this
chapter, to accommodate extended unavailability of the primary site.
Given that SRDF allows read-only access to the remote copy of data, that copy may be used for
backup. The challenge is to establish a point-in-time that gives the backup consistency. This is
accomplished as follows:
• When the time to perform backups arrives, quiesce the application for a short time and ‘flush the
buffers’ so that a consistent set of data, indexes, pointers, etc. exists on disk (both local
and remote).
• Issue a SUSPEND command to SRDF for the volumes that are to be backed up. This command will
allow the applications to continue accessing the local (source) copy of data, but not transmit the
changes to the second (target) copy. However, the changes will be tracked for later transmission.
• Resume the application processing at the local site.
• Take a copy of the selected volumes, using a second processor or a second LPAR accessing the
target volumes.
• When the copy is complete, issue a RESUME command for the volumes. This will allow SRDF to
examine the internal entries for the volumes, and resynchronize the two sets of data by copying
only the changed data across the links.
This technique has the potential to deliver hours of effective, profitable application time to the
installation. The gains in application availability may justify the cost of SRDF in their own right
and disaster recovery capability may be an added bonus. Of course, for this application, the second
copy may be on the same computer room floor as the primary copies or at a remote site.
Synchronization and There are several ways in which the source and target sites may be out of synchronization with
Resynchronization each other. These are:
• At the inception of the SRDF relationship, when initial synchronization is being established.
• In the event that a source or target volume fails and application activity continues using the
surviving volume. (After repair of the failed volume, resynchronization is required.)
• In the event that all physical links are inoperative between the sites. (This may be deliberate
or accidental. In this case, the applications may continue running against the source volumes with
resynchronization taking place after the links are restored.)
• In the event that the user issues a SUSPEND command against specified or all volumes. (In this case
the applications continue running against the source volumes, with resynchronization taking place
after the RESUME command is issued for the SUSPENDed volumes.)
Use of Track Tables SRDF does not keep a copy of every change to a given track. As data is written to a track, only the
latest copy is stored. Within the Symmetrix, a track table exists. This table contains an entry for
every track in the defined environment, describing:
• The location of the track on disk.
• Whether the track image is currently in cache and if so, where.
• Demographic data (dates, etc.) about the track.
• Whether the track image is synchronized with its internal (mirror) or external (target) pair.

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As a track changes and synchronization does not take place (failed volume, absence of links,
SUSPENDed operations), the changed track indicator is maintained. Consequently, a track may
change once or a thousand times in an interval, and only one copy will be stored. The cache is not
filled with historical aged tracks awaiting application to the mirror. Once the track table entry for
a track is marked, the track itself may be destaged to disk by the normal cache management
routines. When it is necessary to perform the resynchronization of a changed track, that track is
copied from cache or retrieved from disk to the local cache if it had been destaged.
In addition to resynchronization, use of track tables also enables mirroring of only those tracks
that have changed since the last update in a multi-hop mirroring solution.
Performance The capability of placing data in two locations does have a performance impact, particularly for
write operations. The performance impact may be lessened or even eliminated based on the mode
of synchronization. The size of this impact is primarily a function of:
• Write activity rate to mirrored volumes
• Average data block size being updated
• Distance between sites
• Type of link (telephone line, ESCON, Fibre Channel, or IP)
• Number of links
• Mirroring mode (Synchronous/Semi-synchronous or Adaptive Copy)
It is possible to model your data and its characteristics to determine the optimal SRDF
performance for your site.
Data Recovery Recovering from a disaster has several components. The target volumes must first be attached to
the recovery host/server. Secondly, they must become read/write-capable. To accomplish this, a
single Symmetrix command must be issued. This can be done:
• By host-based SRDF management software
• At the Symmetrix service processor by a local EMC field engineer
• Remotely by the EMC support center, using a dial-in capability
At this stage, the data can be accessed and complete data center operations can be restarted.
Databases There are no special considerations for database environments apart from ensuring that all the
data necessary for a consistent database is remotely mirrored. Restarting from the remote (target)
copy of data (assuming all the appropriate data is remotely mirrored) is no different from restarting
locally after a power failure.
Backup Using Remote Data Given that SRDF allows read-only access to the remote copy of data, that copy may be used for
backup. The challenge is to establish a point-in-time that gives the backup consistency. This is
accomplished as follows:
• When the time to perform backups arrives, quiesce the application for a short while, and ‘flush
the buffers’ so that a consistent set of data, indexes, pointers, etc. exists on disk (both source
and target).
• Issue a SUSPEND command to SRDF for the volumes that are to be backed up.
• Resume the application processing at the local site.
• Take a copy of the selected volumes using a second processor or a second LPAR accessing the target
volumes.
• When the copy is complete, issue a RESUME command for the volumes. This causes SRDF to
examine the internal entries for the volumes and resynchronize the two sets of data by copying only
the changed data tracks across the links.
This technique can deliver hours of effective, profitable application time to the installation. The
gains in application availability can justify the cost of SRDF in their own right, and disaster
recovery capability may be an added bonus.
This technique involves logical suspension of the remote mirroring function. Accordingly it is very
strongly recommended that the remotely mirrored drives also be locally protected, exploiting
the Symmetrix capability of having a drive both be remotely mirrored and locally mirrored via
mirroring, RAID-S, or dynamic sparing.
Read-Only Access As a general rule, the target volumes should be accessed after SUSPENDing mirroring. This has
to Target Volumes obvious benefits with regard to data consistency. Using the second copy for point-in-time backup is
a clear use for this facility.
Read-only access to the target copy of data is available. Making a volume read-only is an attribute
of Symmetrix. If an update I/O operation is attempted to a read-only drive, the operating system
will encounter an error. Handling errors of this nature must be planned for by the user with regard
to each operating system’s behavior. This facility must be used carefully and in no way represents
generalized, full-function access to this data.
SRDF Testing Validating the SRDF configuration can be extremely useful to customers in determining if they are
mirroring all the necessary data elements. This test can be performed with minimal disruption to
production and without staff travel.
By suspending the SRDF link(s), a simulated disaster can be created. It is suggested that either a
point-in-time backup be taken at this point from the target data volumes, or the TimeFinder
product be used to create a separately addressable copy of data to be used for the disaster recovery
test. It is then a relatively simple matter to run a test of the mission-critical applications at the target
site. In so doing it is easy to identify if everything required is in fact being remotely mirrored and to
verify that the database and application environment can be made ready in a simple, complete, and
timely fashion. Users might also utilize SRDF’s Consistency Group feature for this purpose.
This testing provides reassurance that SRDF delivers the best business continuity and recovery
solution available, and renews confidence in the recovery plan itself.

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34
Chapter 5
Symmetrix Software Solutions and Service
Software Solutions Information Protection — EMC provides software solutions that maintain continuous data
availability. The standard features of Symmetrix software solutions facilitate continuous data
availability in the event of any major system component failure or power outage, and provide the
ability to repair or replace the failed component without any interruption in operation. Symmetrix
software solutions continually perform self-diagnosis to identify and correct potential problems
prior to any disruption of data availability. Software products include:
• Symmetrix Remote Data Facility (SRDF)
• EMC TimeFinder
• Symmetrix Data Migration Services (SDMS)
• EMC Foundation Suite by Veritas and EMC Database Edition for Oracle by Veritas
• EMC CopyPoint
• EMC CopyCross
Information Sharing — Symmetrix offers centralized, sharable information storage for supporting
changing environments and mission-critical applications. This leading-edge technology begins
with physical devices shared between heterogeneous operating environments and extends to
specialized software that enhances sharing information between disparate platforms. These
software solutions include:
• Symmetrix Enterprise Storage Platform (ESP)
• EMC Celerra
• EMC InfoMover
• Application Programming Interfaces
Information Management — Symmetrix consolidates storage capacity for multiple hosts and
servers and improves information management. The EMC ControlCenter family of products
further enhances this efficient, consolidated storage approach. These optional software solutions
include powerful GUI-based tools that simplify Symmetrix configuration, performance, and status
information gathering and management. These products include:
• EMC ControlCenter
• EMC PowerPath
• EMC Data Manager (EDM)
The true power of EMC’s Enterprise Storage architecture comes with the synergy unleashed when
customers utilize multiple EMC products together ñ allowing them to fully harness the power of
their information for the first time and realize The EMC Effect.
For more information about EMC Enterprise Storage solutions, contact your EMC sales
representative.
Professional Services EMC Professional Services consultants provide a full range of services to enable you to extract
maximum value from your information and achieve The EMC Effect. These services assist you in
applying EMC Enterprise Storage concepts and capabilities to your business issues. The EMC
approach enables you to put information at the center of your IT infrastructure so you can take
control of your information and utilize it to your full advantage.
Professional Services help you leverage EMC Enterprise Storage solutions, expertise, and resources
to achieve success faster, more cost effectively, and with less risk. They enable you to:
• Understand your current IT environment and take charge of it.
• Create a more responsive, efficient, and flexible IT infrastructure with information at its center.
• Share, protect, and manage critical information across the enterprise.
• Deploy robust new enterprise solutions faster.
EMC Professional Services personnel utilize EMC Storage Logic™
, a framework of EMC-specific
and storage industry best practices that addresses all phases of an enterprise solution. Use of this
framework ensures consistency and quality of deliverables and facilitates effective management of
project budgets, schedules, and specifications.
To help you build an IT infrastructure that takes full advantage of all your critical information, EMC
Professional Services provides both strategic enterprise consulting services and practical enterprise
software implementation services. Consulting services help you assess your current
infrastructure in light of your requirements and sort through various options. Implementation
services help you integrate a specific hardware and software solution into your unique environment.
Enterprise Business Enterprise Business Continuity services protect and enhance your ability to generate revenue. They
Continuity help you build an enterprise business continuity infrastructure that not only eliminates
unacceptable downtime (planned and unplanned) but also creates new ways to capitalize on
business opportunities to generate increased revenue and customer services. In short, Enterprise
Business Continuity enables businesses to accelerate their entire operation.
Enterprise Business Continuity services help you map and build your infrastructure to satisfy a
range of business continuity requirements from high availability to mission-critical availability to
continuous availability to disaster recovery. Assessment, planning and design, and software
implementation assistance is available.
Use of EMC Professional Services personnel for implementation enables you to quickly realize the
advanced functionality of EMC software, while your in-house IT staff continues with other
revenue-generating activities. A range of SRDF software implementation services are available,
from basic software installation to complex integration projects that encompass the complete
project lifecycle. Regardless of the level of complexity, EMC Professional Services personnel can
address your unique technical, staffing, or timing requirements.
In addition to software implementation services for such key business continuity products as
SRDF, TimeFinder, and EDM, implementation services are also available to help you expand your
information sharing, management, and protection capabilities by adding other EMC software
products to your infrastructure.

36
Enterprise Storage Enterprise Storage Architecture and Design is the most consultative practice. Its services give you a
Architecture and Design broad-based overview of your IT environment and indicate where and how enterprise storage can
— Building an enhance it. Assessments recommend specific storage-related initiatives that can help you compete
E-Infostructure in your marketplace or otherwise increase the value and effectiveness of your infrastructure. An
E-Infostructure employs EMC products so that customers are prepared to address the realities of
the new E-based economy.
Enterprise Storage Network Enterprise Storage Network services help you break out of current network limitations. They help
you cost-effectively consolidate information from heterogeneous sources to offload data
movement from your general-purpose network and improve information protection, sharing, and
management. EMC experts in this new field of storage networking help you assess, plan, design,
and implement an Enterprise Storage Network infrastructure that addresses today’s requirements
and can grow with you in the 21st century.
Support and Service The EMC Customer Support Center, headquartered in the United States, directly supports EMC
software products. The following telephone numbers offer technical support:
U.S. (800) 782-4362 (SVC-4EMC)
Canada: (800) 543-4782 (543-4SVC)
Worldwide: (508) 497-7901 (or contact the nearest EMC office)

EMC SRDF
EMC Corporation
Hopkinton
Massachusetts
01748-9103
1-508-435-1000
In North America
1-800-424-3622, ext. 362
EMC2, EMC, and Symmetrix are registered
trademarks and TimeFinder, ControlCenter,
E-Infostructure, SRDF, FarPoint, Enterprise
Storage Network, Connectrix, and where
information lives are trademarks of EMC
Corporation. Other trademarks are the
property of their respective owners.
© 2000 EMC Corporation. All rights reserved.
Printed in the USA. 6/00.
Produced by EMC Global Communications.
L759.2
Product Description Guide
www.EMC.comwhere information lives

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